1. Technical Field
The present invention relates to a curved surface machining method and a curved surface machining apparatus, wherein a high-speed fluid is sprayed onto a workpiece in an abrasive-containing solution into which an abrasive has been admixed, and the surface of the workpiece is ground to an intended surface roughness and profile accuracy.
2. Description of the Related Art
In structural components requiring long-term durability such as artificial joints, for example, the profile accuracy and surface roughness of opposing sliding surfaces have a marked effect on the abrasion resistance of these surfaces. In conventional practice, manual procedures that use a V-type grindstone, a toroid grindstone, or a spherical grindstone have been used in curved surface machining for these spherical surfaces or non-spherical surfaces. However, finishing a desired curved surface requires a great deal of skill and has not been something that anyone can easily accomplish. Furthermore, time is required to finish the surface, and mass production has not been deemed feasible.
Machining a curved surface such as a sliding surface in an artificial joint requires not only accurately finishing the surface to the necessary profile accuracy, but also performing smooth finishing to an extremely low surface roughness. One method of curved surface machining involves mixing an abrasive into a high-speed fluid and spraying the resulting material onto a machined surface, as seen in Japanese Patent Application Laid-Open (Kokai) No. 2000-158344, but this approach has problems in that the abrasive causes wear and clogging in the nozzle for spraying the high-speed fluid. Furthermore, a large amount of the abrasive is needed, and the abrasive sometimes scatters into the surroundings.
Therefore, a method is proposed in which a workpiece is set in an abrasive-containing solution into which an abrasive has been admixed, and a water jet is sprayed in this solution, so that the abrasive in the mixture is sprayed onto the workpiece, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 2002-113663.
While this method has advantages in that a small amount of the abrasive is sufficient and the abrasive does not scatter into the air because the abrasive can be used cyclically in the mixture, an object of the machining in this prior-art example is foreign matter removal such as deburring and deposit removal. Consequently, precise machining aimed at improving the surface roughness or dimensional accuracy of a curved surface cannot be accomplished. Above all, the method in the prior-art example described above causes additional damage on the surface of the workpiece because an abrasive with a grain size of 1 μm or more is used, which is unacceptable even in terms of surface roughness alone.
A machining apparatus for performing such machining is described in the above-mentioned prior-art example. However, from the standpoint of the machining purpose (i.e., performing deburring or deposit removal) as well, this apparatus is provided only with a rough control mechanism. It has probably been assumed that translational three-dimensional control of the nozzle for spraying the high-speed fluid would suffice, and that, at most, adding rocking or horizontal rotation of the nozzle would be adequate. However, such a control function is insufficient for improving the surface roughness or profile accuracy of a curved surface.